1. Field of the Invention
This invention relates generally to electric generators and more particularly to electrical generators powered by utilizing part of the mechanical energy of a rotating wheel.
2. Description of the Prior Art
It is often desired to have a source of electrical power present at the wheels of a car, truck, or other motorized vehicle. For example, electronic wheel monitoring devices used to detect tire underinflation or tire overheating require a local, dependable source of electrical power. Other devices designed to improve the appearance, performance, or safety of the vehicle, such as wheel rim lights, also require a source of electrical power at the wheels.
A conventional solution to this problem has been to run wires from the vehicle's battery, or from an auxilliary battery, to each of the wheels. A disadvantage with this solution is that a commutator is required to transfer the electrical power from the wires attached to the vehicle's stationary frame to the devices attached to the rotating wheels. As is the case with all mechanical devices with moving parts, commutators have a tendency to wear, malfunction, and eventually fail.
If an auxilliary battery is used another problem that can occur is that the battery might become discharged unbeknownst to the vehicle operator. If the operator was acting in reliance to devices powered by the auxilliary battery potentially dangerous situations might occur.
In an attempt to overcome the above mentioned problems, various types of electrical generators have been coupled to the wheels of a vehicle. For example, one type of generator is coupled directly to the wheel axle and another type has a small friction wheel which contacts the vehicle's tire and rotates with it. A problem with external generators of this type is that, again, it is necessary to utilize commutators to couple the generator's output to devices affixed to the rotating wheels.
In U.S. Pat. Nos. 3,699,367 and 3,760,351, Stephen E. Thomas discloses two generators that fit within the tire of a car's wheel so as to be able to directly power sensors, monitors, or other devices disposed therein. One advantage of Thomas' devices is that the need for a commutator is eliminated.